PROJECT SUMMARY Therapeutic intervention for prenatally diagnosed craniofacial defects holds promise for improved quality of life. Early detection, however, requires an improved understanding of the genetic factors underlying the craniofacial dysmorphologies. We have recently identified a role for MDM2, a ubiquitin ligase that negatively regulates the p53 tumor suppressor protein, in craniofacial development. Mice hypomorphic for Mdm2 exhibit craniofacial defects including cleft palate that are strain-dependent, suggesting that these genetic backgrounds encode variation at modifier loci which affect craniofacial development and the severity of craniofacial anomalies. The overall goal of this project is to obtain detailed information about the head and face phenotype of Mdm2 hypomorphic mice, which will guide future mechanistic studies of craniofacial development and form the basis for unbiased, forward genetic approaches to identify novel modifiers of craniofacial malformation. In Specific Aim 1, we gain insight into the cells, tissues, and structures altered by low MDM2 expression by quantifying the craniofacial dysmorphologies in Mdm2 hypomorphic mice. In Specific Aim 2, we examine the gene regulatory networks underlying the penetrance and expressivity of craniofacial anomalies in Mdm2 hypomorphic mice by obtaining detailed information about the differences in gene expression in embryos on the sensitized and nonsensitized genetic backgrounds. Together, our studies contribute to the mission of the National Institute for Dental and Craniofacial Research (NIDCR) to develop new early detection and personalized therapeutic intervention strategies for craniofacial defects by yielding new understanding of the gene and protein networks that govern craniofacial development and by providing new insight into how perturbing these networks influences clinical severity.